The Incidence of Winching

........Really Big Things!

 

There have been many conversations both on and off line, and on several Jeep forums around the net asking or discussing or dissenting or out and out saying this winch pull just below could never be done with a Jeep. Some debate it and some offer their own magical math to justify one way or another how this could or could not be accomplished with so light of a vehicle as my Jeep CJ-7.

Suffice to say, no, a stock Jeep or even a heavy wrecker is not going to pull the concrete truck, as is, where it was, under the conditions it found itself when finally incapacitated as a stuck. But, with experience, modifications, and know how, you CAN do this. Below is how to set up your rig for this and how to rig your blocks and cables to make this and other kinds of unbelievable pulls.

At the bottom of this page is phone number contacts for verification if the few still don't believe these photos and the job of pulling out a 66,000 concrete truck is possible...............

 

 

........Back in the good 'ol days.....

where it began for me, 40 years ago.....

 

Well, here in this photo above, there is a shot of a Ramsey 4000 lb. hand crank winch and boy, was that a major effort in trying to pull out my Jeep from a stuck with that miserable thing. It looks good on paper, but in application it was miserable indeed.

This is my 2nd Jeep, it was 1967 and I was 14 then. I look bluesy because I just got off the summer from logging with a 1937 CAT RD-7 in the Sierras and was heart broken that in a week, school would start again. I wanted to run CATs and go jeepin' and chase maidens and school could not possibly be factored into those desires..........(See Jeep Page 24 for what it was like logging as a kid back then).

Note too those strange recaps tires and the tread on my Jeep. It was surely different back then.........

 

........Now, how'd the Jeep do this.........?

Read on....

 

Here is the rig up, below, how this was rigged off to accomplish this feat.

 

Rigging up

This was the re-pull, so only used 2 blocks for this.

Almost ready.

Viola, it's out and on its own again. Okay, this is the re-pull event whereby we restaged the pull. Here, the truck only had a few yards of sand in it and its weight was about 57,000 lbs. I used two blocks giving me 48,000 lbs of pull from a 12,000 lb. winch. The winches were MegaWinches.

 

 

These diagrams above show how it is done and the ratio of pull for each added snatch block in the line, as long as they remain a few degrees of parallel of each other as shown.

 

 

But no, you cannot do this with any stock vehicle, period! If you try it you will rip your rig apart, literally. If the winch is not fastened properly, you will rip it from the mount and do extreme damage to vehicles, mission and crews. Careful now. Here we see the schedule 80 2x4 bumper, gusset plate and other add ons that make for the frame and bumpers competent to stand up to this sort of use. The blocks are 35 ton rating. That is sheer failure not rolling load failure for rating.

You do need these 35 ton industrial snatch blocks, and not any of those offered by the off road companies or light winch suppliers. They will fail miserably. Also, DO NOT EVER use flexible nylon tow straps anywhere near a winching operation. Use chain as chain does not store energy on release, but drops harmlessly to the ground upon failure. Here, see this formulae for this application and effect:

 

modulus of elasticity (E) (Young's modulus)
E relates stress to strain for a linear elastic material:
stress = E * strain
It is expressed in force per unit area, usually pounds per square inch or kilograms-force per square centimeter. The strain may be a change in length. Young's modulus; a twist or shear, modulus of rigidity or modulus of torsion; or a change in volume, bulk modulus. In the SI, all types of moduli of elasticity are reported in pascals, the conversion factor being one psi = 6.894 757 E+3 pascals. Also known as ELASTIC MODULUS and YOUNG'S MODULUS.
Chain stores more for strength, releases 100% in the links' space between each chain couple when failed or released, thus no modulus expressed in the form of violence as a tow strap.

 

Here is a CAD drawing of the addon modifications to VEX's frame to allow for this type of pull, when called upon to do so, or when needed. Note the over engineering for the fact that one must also factor in torque and cross sheer when pulling, since no pull is perfect line of sight. Photos of this arrangement are below.

 

 

Here we see the gussets from frame to bumper as shown in the diagram above on the rear bumper set up.

 

 

Here we see the insert of plating that runs on the inside of both frame rails.

 

 

Here is the rear winch mounting configuration.

 

 

 

And here in these two photos above is the setup as is, in 2005.

 

 

How To Rig A Snatch Block.....

And can you really get a 2:1 advantage when using one......or two,........or three.................?

Yes!

 

What's a snatch block? I've seen several winching accessories, but don't recall one being a snatch block?

A Snatch block is an opening block that clevis' shut or open with various devices. It allows for one to insert a cable into the block itself without re-threading or taking the hook off the cable end or inserting the cable into the block at the end of the winch line. It is a highly flexible 2:1 increase of pull device.
   
By looking a th diagrams on this page, once can see the by adding one or two or more blocks, depending on rolling or static block application it is possible to increase pull by a factor of 2, or 3 or 6 or even more to a factor of one. Or, at the limit of sheer failure or castastrophic failure (shock-sheer). In the ned diagrams of description you can see the application of a 'static' block rig up and a 'traveling' block set up. In both, there is a tremendous difference in pull and application, but in each, a snatch block can save the day when rigged properly.
 
Here is the table from the Crosby Group catalog of how angles and diect parallel line of pull effects the available load of the winch's capacity in a given situation.:
 
Angle is the measured angle between the legs of the line as they pass over the block sheave. Factor is the multiplier for the applied line load to calculate the block load.
 
Angle
Factor
0
2
10
1.99
20
1.97
30
1.93
40
1.87
50
1.81
60
1.73
70
1.64
80
1.53
90
1.41
100
1.29
110
1.15
120
1
130
0.84
135
0.76
140
0.68
150
0.52
160
0.35
170
0.17
180
0

In #1 above, the angle is 90 degrees, so the factor is 1.41. So a 10,000 pound load will place 14,100 pounds of force on the block/anchor.
And in #2 above, if the bitter end of the line is not hooked to the winched vehicle but is hooked to a tree or rock next to it, for each pound of winch force applied, the block will be under *twice* the load, while the line strain will be equal to the line pull. So if you apply a full 12,000 pounds of pull, you are putting 24,000 pounds of stress on the block/anchor.   If, however, the bitter end *is* attached to the winched vehicle, the block becomes a "traveling block", even though it is attached to a solid object, because the vehicle itself is actually doing the "traveling", and the load on the line is halved, since you are using two lines to "support" the load.   In this case, the mechanical advantage is 2/1, so you get 2 pounds pull for each pound of winch effort. Now, since you have two lines splitting the load, let's say it's 10,000 lbs. (you're really stuck), the line load is halved to 5000 lbs per line, but the *block* load is still 10,000 lbs because of the parallel line angle factor of 2.   As you can see, while the load on the winch is cut in half, as is the line speed for winding, the load on the block is not, and is equal to the total line load.
 
This is why using a properly rated and carefully maintained block is of the utmost importance when winching. In most RV winching situations, "double-lining" is the best method to reduce stress and strain on the lines and winch motor, at the expense of speed, but may be the worst thing you can do from the safety or block standpoint, if your block is not adequately rated or is in poor condition or if you don't know the strength of the anchor or the stall-pull of your winch. The block is being subjected to twice the force of any of the other components, and consequently the winch operator may never know he is exceeding the capacity of the block until it parts and takes his head off. This is especially true when using very powerful winches.  

Imagine the stress on a block (and it's anchor as well) when the SUV owner with the Warn 12,000 lb winch double lines to pull his vehicle over an obstacle and sticks a wheel behind a rock, locking the vehicle in place. The winch is already rated for 6 tons single line pull, and adding a traveling block doubles the pulling force to 12 tons. If your snatch block is (as many are) underrated for the winch/line combination, and you have a 6 ton rated snatch block, or even a "really big 8 ton-rated" block, which is commonly sold with RV winches, you still have the potential of block failure because you are using a 6 - 8 ton block with a system capable of exerting 12 tons of force under circumstances where you might not recognize the actual pulling force you are exerting, because you are not really stressing out the winch.  

A recipe for disaster.  

This is even more true of hydraulic winches, which, unlike electric winches, usually pull until something breaks. With an electric winch, there is a built-in "safety" mechanism which is that near the maximum-pull winch-stall load, the motor draws enormous amounts of amperage and heats up quickly. This means that the motor will usually stall due to lack of available amperage, increased electrical cable resistance due to heating, or motor overheat long before one can actually reach the rated pull, which is determined under lab conditions.  

With a hydraulic winch though, the hydraulic motor runs happily along, getting slower and slower, and exerting more and more force, until something snaps, and will *rarely* stall before reaching breaking load.   So, one must be *extra* careful when using hydraulic winches, since the winch appears to be quite happy, and is just getting slower and slower, and the typical RV person expects it to stall, which it won't.  

Please keep in mind that we are always talking about the "safe working load limit" here, and while the ultimate failure safety limit is typically 5 times the working load limit for commercially-rated hoisting gear, it may be less, or non-existent in cheap, uncertified blocks, particularly surplus blocks available at low price.  

I get my blocks from here, locally or by mail order:

http://catalog.thecrosbygroup.com/BODY_314.HTM - Snatch Blocks, Logging and Heavy Industrial

http://catalog.thecrosbygroup.com/maininterface.htm - The Crosby Group Home Page

 

If you would like to speak to a technician-engineer that can also help and verify this data herein, here is the contact information at The Crosby Group:

Brad Beall
Product Engineer, The Crosby Group
bradbeall@thecrosbygroup.com
phone: 918-834-4611 x322
fax: 918-834-9447

 

 

The Different Blocks and the Different Rig-Ups

 

To begin this part here is some photos of the different blocks available that are heavy duty and that I use in my applications, from everything to pull out fellow Jeepers to pulling concrete trucks, road graders, combines, etc.

This is Stainless Steel, single sheave for doubling the pull, and for those that have an aversion to orange. But the orange color has a reason in that it is easier to find in the woods in snow or anywhere since these things seem to wander off after use........

Here is a 'double block' if one wants to triple the pull using only two blocks. The other would be like the first block above: single sheave.

Here is the triple shave block for tripling the line pull. This is a serious block.

This is a logging type of double sheave block of a capacity of about 20 tons

This block is a single sheave for a single line pull of about 23 tons rolling-lift, pull.

This block is single sheave but far more serious, getting up to 28-30 tons of rated load.

This is far more serious block.

This is more the type and capacity block I use in my pulls. You are getting up to the 35 to 40 ton range and this is about right for our heavier applications.

 

 

Getting ready to 'Traveling Block', or, 'Running Block' rig up as the diagram examples above, to 'par buckle' the Jeep behind VEX down the trail some and out of its stuck. I buried my Jeep first, right to the frame and then some as a dead man affair, so that I could counter resistance and pull out the Jeep stuck behind the guys standing there. After the stuck Jeep was out, with running chains and ARBs on my Jeep, VEX raised up and drove back onto the main trail on its own without winching myself.

 

Static Block Vs. Traveling Block Rig-Ups

 

In this diagram above we see the configuration of a traveling block rig up verses a static block rig. In the one on the right is how the concrete truck got unstuck with the Jeep in the first pull out (not the staged repull as shown in the photos at the top), while the one on the left is how most of us, when stuck bad, get ourselves out whereby the Jeep moves and not the anchored static load.